1. Field of the Invention
The present invention relates to the imaging of lithographic plates and, more particularly, to conditioning a lithographic printing plate substrate for imaging in conventional, commercially available electrostatic or ink-jet printers.
2. Background Information
Imaging of lithographic printing plates by electrostatic or ink-jet printing has been the subject of extensive research and development and has been commercialized to some extent. In the case of electrostatic imaging, a toner is applied to an electrostatic image formed on a lithographic plate substrate and is then fused. Similarly, the desired image can be formed and then fixed on a suitably prepared substrate by ink-jetting a fluid. The toner or ink-jet image on the substrate is either receptive or repellant to a printing ink, depending on the nature of the surface of the plate substrate to which the image is applied and fixed. The substrate may or may not include a coating suitable for receiving the toner or ink jet fluid. An important advantage of electrostatic or ink-jet imaging is the current availability of machines (electrostatic copier/printers and ink-jet copier/printers) that can be readily adapted for use in imaging lithographic plate substrates.
Lithographic printing machines and processes require plates that are highly dimensionally stable and durable, which inherently makes them relatively stiff and hard. Although coated paper substrates and high-density plastic substrates are commonly used to make lithographic printing plates, metals, such as aluminum, tin and copper, are generally preferred because of their high dimensional stability and durability.
Metal plate substrates are usually prepared from metal sheet material supplied in large rolls. After any required finishing and coating treatments of the sheet material in roll form, the roll stock is slit and cut into sheets of the desired size. The slitting and cutting frequently leaves the sheets with sharp, jagged edges. Even if plate substrates are supplied to printing shops with smooth edges, some plate-makers re-cut the plates, often using office-type guillotine paper cutters. Substrates cut down by printing shops (the users of the plate substrates) are virtually certain to have rough, sharp edges, burrs and other irregularities.
Many guide and sheet-transfer components of electrostatic and ink-jet printer engines are made of or coated or covered with relatively soft materials. When harder materials with sharp, rough edges are fed through the printer engines, the soft components are subject to rapid wear and in some cases immediate and costly damage. Moreover, sharp, jagged edges, burrs, and other irregularities along the edges of sheets of hard materials can lead to miss-feeding and jamming of the printer engine.
An object of the present invention is to provide an article suitable for imaging in currently available electrostatic and ink-jet printer engines to make a lithographic printing plate. More particularly, it is an object to condition a lithographic plate substrate so that it will be reliably inducted and transported by the sheet-transports of such printer engines without causing wear or damage to the printer engine. It is also an object to provide a plate substrate that is conditioned in a very simple, economical and effective way to feed properly through printer engines for imaging without miss-feeding or jamming.
As used hereinafter, the term xe2x80x9cprinter enginexe2x80x9d means an apparatus that is capable of transporting sheet material and forming an image on the sheet material by placing a substance on the sheet material by electrostatic or ink-jet deposition.
The objects referred to above are attained, in accordance with the present invention, by an article for use in preparing a lithographic printing plate by imaging in a printer engine. The article includes a metal plate substrate in the form of a sheet having opposite faces and edges and an edge protector adhered along at least one edge of the plate substrate, the edge protector being of a flexible material, being coextensive with the edge, having face portions adhered to portions of the opposite faces adjacent the edge, and having an edge portion overlying the edge.
The edge protector ensures that the article to be imaged in a printer engine is entirely free of sharp edges that can scratch, cut, or abrade the guide and transport components of the printer engine and that can cause miss-feeding or jamming of the article in the printer engine. Edge protectors can be provided on one or all edges of plate substrates at a relatively nominal cost. Thus, even if the metal stock is slit and cut by processes that leave smooth edges, incorporating edge guards provides further assurance against problems in imaging the plate substrates in printer engines without adding significant costs. It may also be possible to reduce the costs of slitting and cutting sheets for the plates and following less rigorous quality control procedures, thereby allowing cost reductions. In instances where printing shops cut down plates substrates to meet their requirements, some embodiments of the present invention are well-suited to conditioning of the cut-down sheets by the plate makers.
One form of edge protector is a coating of a flexible resin substance. Alternatively, the edge protector may be an elongated band of flexible material folded over the edge and adhesively bonded along at least the face portions to the portions of the opposite faces adjacent the edge. A particularly simple and cost-effective form for an elongated band is a self-sticking adhesive tape. The adhesive tape, preferably, has an adhesive that is detachable from the plate substrate without marring the plate substrate, so that the edge protector can be removed from the plate after imaging. An adhesive tape having a paper base is often advantageous for use on plate substrates that are imaged in electrostatic printer engines, inasmuch as the possibility of melting or softening of the base and/or adhesive in the fuser of the printer engine is eliminated.
According to another aspect of the present invention, a method of preparing a lithographic printing plate for imaging in a printer engine includes the step of forming an edge protector along at least one edge of a plate substrate, the edge protector being of a flexible material, being coextensive with the edge, having face portions adhered to portions of the opposite faces adjacent the edge, and having an edge portion overlying the edge.
The foregoing description has outlined rather broadly some features and advantages of the present invention. The detailed description of embodiments of the invention that follows will enable the present invention to be better understood and the present contribution to the art to be more fully appreciated. Those skilled in the art will recognize that the embodiments may be readily utilized as a basis for modifying or designing other structures and methods for carrying out the purposes of the present invention. All such structures and methods are intended to be included within the spirit and scope of the invention as set forth in the appended claims.